Bisphosphonates (BPs) are widely prescribed anti-osteoclastic medications. The intravenously administered BPs pamidronate and zoledronic acid are used in oncology to control bone metastasis and hypercalcemia. Oral BPs are used to control or prevent bone loss in osteoporosis, including osteoporosis associated with menopause. An estimated 3 million American women are currently being treated with oral bisphosphonates [1]. The monoclonal antibody Denosumab is also used to treat these conditions.
BPs are synthetic analogs of pyrophosphate that readily localize to bones due to their affinity for hydroxyapatite, and reduce osteoclastic activity. They are not readily metabolized, and thus, have long-lasting effects that might extend for several years. BPs are especially attracted to, and localize in, areas of the bone undergoing inflammation or resorption. They are subsequently phagocytozed and internalized by osteoclasts. These internalized bisphosphonates, in turn, trigger apoptosis (cell death) of the osteoclasts, thus inhibiting osteoclast-mediated bone resorption [2]. Osteoclasts seem to be affected by BPs both in terms of number and function. Animal studies have also demonstrated some antiangiogenic properties, which may partially explain the development of osteonecrosis due to limited healing ability of the bone because of reduced vasculature [3].
BPs, especially zoledronic acid, have been associated with a serious adverse effect, osteonecrosis of the jaw. According to the American Association of Oral and Maxillofacial Surgeons (AAOMS), BP-related osteonecrosis of the jaw (BRONJ) is defined as exposed bone in the maxillofacial region for more than eight weeks in patients treated with a bisphosphonate that have no prior history of radiation therapy to the jaws [4]. The non-healing exposed necrotic lesions may involve the mandible or the maxilla or both, and can be painful, persistent, and resistant to treatment. The incidence of BRONJ varies in different studies. BRONJ affects as many as 5-10% of zoledronic acid users and far fewer users of oral bisphosphonates.
Osteonecrosis of the jaw has also been reported in association with denosumab treatment [29]. It would be desirable to identify individuals who are at risk for developing osteonecrosis of the jaw, so that subjects at greater risk could be considered for alternatives to anti-resorptive therapy or, if suitable alternatives are not available, could be monitored more closely.